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Specifying the resource libraries

Design Libraries ModelSim EE/PLUS Reference Manual

Predefined libraries

Certain resource libraries are predefined in standard VHDL. The library named

std

contains the packages

standard

and

textio

, which should not be modified. The

contents of these packages and other aspects of the predefined language

environment are documented in the

IEEE Standard VHDL Language Reference

Manual, Std 1076-1987

and

ANSI/IEEE Std 1076-1993

. See also, "Using the

TextIO package" (p425).

A VHDL

use

clause can be used to select specific declarations in a library or

package that are to be visible within a design unit during compilation. A

use

clause references the compiled version of the package—not the source.

By default, every design unit is assumed to contain the following declarations:

LIBRARY std, work;

USE std.standard.all

To specify that all declarations in a library or package can be referenced, you can

add the suffix

.all

to the library/package name. For example, the

use

clause above

specifies that all declarations in the package

standard

in the design library named

std

are to be visible to the VHDL design file in which the

use

clause is placed.

Other libraries or packages are not visible unless they are explicitly specified

using a

library

use

clause.

Another predefined library is

work

, the library where a design unit is stored after

it is compiled as described earlier. There is no limit to the number of libraries that

can be referenced, but only one library is modified during compilation.

Alternate IEEE libraries supplied

The installation directory may contain two or more versions of the IEEE library:

•

ieeepure

Contains only IEEE approved std_logic_1164 packages (accelerated for

VSIM).

•

ieee

Contains precompiled Synopsys and IEEE arithmetic packages for the std_logic

base type, which have been accelerated by Model Technology.

You can select which library to use by changing the mapping in the

modelsim.ini

file. The

modelsim.ini

file in the installation directory defaults to the

ieee

library.